WIP: port to firefox 

I'm creating this PR to start discussing if it is an interesting change to be cleaned up and merged upstream.
 
"AngularJs Batarang ported to Firefox DevTools" WIP prototype: 

- [x] devtool panel and dom inspector sidebar prototypes
- [x] run addon and build xpi from grunt tasks (grunt run_xpi, grunt build_xpi)
- [x] introduce "firefoxExtension.js" to polyfill module "chromeExtension" module
- [ ] cleanup changes
- [ ] test chrome addon built from grunt task (needed to preprocess panel.html on Firefox/Chrome builds)